Production of low pour fuel oils

ABSTRACT

Low pour fuel oils are obtained by first converting waxy pour residua into the corresponding viscous pour residua by deep vacuum fractionation, with or without auxiliary visbreaking or thermal or catalytic cracking, and then blending with sufficient low pour cutter stock to produce fuel oils having commercially acceptable viscosities and pour points.

United States Patent n91 Youngblood et al.

[ Oct. 23, 1973 1 PRODUCTION OF LOW POUR FUEL OILS [75] inventors:Douglas J. Youngblood, Groves;

Thomas A. Cooper, Port Arthur; James H. Colvert, Houston, all of Tex.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: June 25, 1971 [21] Appl. No.: 156,771

[52] U.S. Cl 208/92, 208/15, 208/93, 208/106, 208/364, 208/366 [51] Int.Cl ClOg 37/00 [58] Field of Search 208/15, 72, 93, 106, 208/366, 92, 364

[56] References Cited UNITED STATES PATENTS 2,762,754 9/1956 Offutt etal. 208/106 VACUUM DlSTlLLATlON 3,575,843 4/1971 Aitken et al. 208/933,254,020 5/1966 Frayer et al.

2,900,327 8/1959 Beuther 208/366 2,663,675 12/1953 Ewell 208/1 53,303,128 2/1967 Peel et al. 208/15 Primary Examiner-Herbert LevineAtt0rneyThomas l-l. Whaley et al.

[57] ABSTRACT 5 Claims, 4 Drawing Figures GAS TO RECOVERY L GASOLINEWAXY 1 CRUDE TwR, FURNACE OIL OR DIESEL FUEL WAXY GAS OIL PORTION FORINTERNAL CONSUMP- 4 a o TION 550-650 F I.B.F.

CUTTER 5 'FUEL OlL RESIDUUM minimums Ian 3. 767; 564 SHEET 10F 2 ggumOIs TI LLATION GAS TO REcOvERY L GASOLINE WAXY' 1 7 CRUDE TWR. FuRNAcEOIL OR DIESEL FUEL WAXY GAS OIL PORTION FOR INTERNAL CONSUMP- 4 TION550-650 F I.B.F. A

CUTTER 5 I vIscOus POUR I FUEL OIL REsIOuuM GAS T0 RECOVERY I I V IGASOLINE ATM. i WAXY TWR FURNACE OIL OR c uOE DIESEL FUEL 550'650F EP NCRACKED PROOucTf l6 l4' ATM. I I FLASH WAXY GAS OIL V TWR. PO T ON FOR 4INTERNAL CONSUMPTION .TwR. VISBREAKING I9 HEATER VISCOUS POUR I FUEL OILVACUUM DISTILLATION mfiififlw VISBROKEN RESIDUUM PAIENIEUnuzz: ma3.767.564

CRACKING HEATER ZLze 27 GAS BY PASS -GASOLINE v ATM (FuRNAcE OIL oR}ATMRED. i DIESEL FUEL CRUDE g 22 VISBREAKING HEATER VAC./24 CUTTER 23Lvlscous POUR y FUEL OIL RESIDUUM VISBREAKING WITH RECYCLE THERMALCRACKING 55o-e5oF 35 GAS GASOLINE ATM FURNACE OIL VAC. FCCU I OR gm- 3sDIESEL FUEL 55o"s5oF I.B.P. RECYCLE VISCOUS POUR RESIDUUM FUEL OIL MILDCATALYTIC CRACKING 1 PRODUCTION OF LOW POUR FUEL OILS This inventionrelates to the productionof fuel oils of commercially acceptableviscosities and pour points from waxy crudes such as Libyan crudes. Theinvention includes methods whereby residual fractions obtained from suchcrudes by vacuum fractionation, with or without visbreaking, catalyticcracking or other auxiliary treatment, are converted by blending withlow pour point cutters into fuel oils having acceptable viscosities andunexpectedly low pour points.

Waxy crudescan be defined as those whose atmospheric reduced crudes havehigh pour points and which cannot be converted into fuel oils meeting aprescribed pour point specification (50F. or lower for low By ourinvention fuel oils meeting the viscosity and pour point requirementsconventionally required in the United States can be obtained from waxycrudes by blending their viscous pour residua wit-h certain diluentshereinafter defined as low pour cutter stocks. We

"have discovered that blends containing these low pour cutters exhibittwo unexpected and hlghly important properties.

The first of these is that their pour points are much oilower (usuallymore than 50F. lower) than would be expected frOm calculations based onlinear blending of component pours. This is illustrated by the followingtable wherein 1,020F.+ Libyan residua are blended with the +F. cuttersused in U.S. Pat. No. 3,303,128

5 and with low pour cutters having a pour point of -l 0F.

*The wt. percent of cutter and actual pour points are taken from Table 2of the patent.

* *Calculated pour of blend obtained by linear blending of componentpours.

pour point fuel oils) without using so much cutter oil as to reduce theviscosity of the resulting fuel oils to an unacceptably low level.Viscous pour residua are those whose pour point is primarily due totheir viscosity whereas, on the other hand, waxy pour residua are thosewhose pour points are primarily due to their wax content. Fora givenviscosity residuum, a waxy pour residuum will have a higher pour pointthan a viscous pour residuum because the wax present therein will causeit to solidify at a higher temperature.

U. S. Pat. No. 3,303,128 describes a procedure for converting waxycrudes into fuel oils that meet come mercial requirements in Great.Britain, where relatively high pour points are tolerated. This patentshows that a maximum pour point of 70F. and a viscosity range of 40 to90 cs at 75C. can be obtained by vacuum dis-;

tillation of waxy crudes under conditions to obtain a final vacuumresidue boiling above 550C. (1,022F.) at a pressure corrected to 760 mm.Hg but below the temperature at which cracking of the feedstock corn-;mences. The patent shows that when this is done the heat-modifiedresidues can be blended with a typical; catalytically cracked gas-oilcutter stock, having a pour point of 20F., in proportions such that theresulting fuel oil will meet British specifications. g

In the United States, most fuel oils must have viscosi-I ties of about50 to 240 Saybolt Universal Seconds; (SUS) at 210F. and a pour point of50F. or less. This} combination is considerably more difficult toobtain: than the British requirements mentioned above. For ex-; ample,Table 2 of the patent shows that with a Nigerian crude residue a fueloil having a 40F. pour point is obtainable only after vacuumdistillation to a TBP cuti point of 595C. (l,l03F.) followed by cuttingthe resi-} due with 52 percent by weight of gas oil and that this. pourpoint could not be reached at all with a Libyan. crude, even whendistillation temperatures as high asl 1 to 550F. They can also beobtained by other proce- The second advantage possessed by our low pourcutters is that they are effective with a much wider range of viscouspour residua than could be used with the cutters previously employed.Thus, Libyan virgin crudes need be distilled only to 950F. or higherresidua, and

by the use of visbreaking the depth of fractionation required to obtaina residuum that will blend with a low pour cutterto meet fuel oilrequirements can be still further reduced. To obtain a suitable fuel oilfrom less waxy crudes, such as Mata crude, the virgin residuum need beout only to a 850F. or higher lBP. This advantage will be furtherdescribed and illustrated with reference to the accompanying drawings.

We have found that the above and other advantages 1 are obtained byusing cutters with pour points between herein designated as low pourcutter stocks. It is an im- 5 portant advantage of the invention thatthey may be obi tained from the same stocks vused 'in producing highpour cutters, having pour points on the order of +20F. or higher, byreducing the end point of the distillation.

E in which they are produced. To illustrate this, light gas 55 oilsobtained from the total liquid product from oncethrough visbreaking ofLibyan reduced crude were tested for pour points. The 350-550F. fractionhad a 30F. pour point and the 350650f. had a +5F.

pour point. Thus a 35F. lower pour point cutter was obtained by reducingthe cutter end point from 650F.

dures such as thermal cracking, catalytic cracking, visbreaking and thelike. Representative cutter stocks obtained by these procedures arefurther described in Ex- The amount of cutter to be mixed with viscouspour residua will depend largely on the fuel oil specifications tha tmust be met. Since cutter stocks are normally worth more than the fueloils into which they are blended, it is desirable to add only enoughcutter to meet maximum viscosity specifications as well as the 50F.maximum pour point mentioned above. Within these limits the exact amountwill vary with the particular viscous pour residua being treated and thetype of cutter stock used, but will usually be within the range of about15 percent to 45 percent by weight and, in most cases, within thepreferred range of 20 percent to 40 percent, based on the weight of themixture of residl uum and cutter. It is understood that in the preferredpractice of the invention, a waxy crude is first pretreated by vacuumdistillation, with or without an auxiliary treatment such as visbreakingthermal cracking or' both, or catalytic cracking, to convert its waxypour re-, siduum into viscous pour residuum after which this vis-' couspour residuum is blended with an amount of a low pour cutter sufficientto produce a fuel oil having a maximum pour point of 50F. and aviscosity within the range of about 50 to 240 SUS at 210F. The preferrednew fuel oils of the invention are those produced by this procedure.

In addition to the advantages outlined above, our invention also makesavailable a source of low sulfur fuel oils of great commercialimportance. This is because waxy crudes normally have low sulfurcontents. This is shown in the following tabulation where 30 weightpercent of cutter was added to various residua from waxy crudes and thesulfur content of the resulting blends was determined.

No. Waxy Resid Cutter Fuel Oil Blend Crude Type Type Sulfur, Wt.

l Libyan I020F. 350650F. 0.72

Virgin VisbrOken 2 Libyan 850F.+ do. 0.60

visbroken 3 Mata 850F.+ 350650F. L36

4 Nigerian I020F.+ 350650F. 0.43

Virgin visbroken 5 Orito 1020F.+ do. 1.00

Virgin I Our invention also includes certain processing procedures inwhich our low pour point blending is applied on a commercial scale. Thesimplest of these is vacuum distillation by the procedure showndiagrammatically in FIG. 1 of the drawings, wherein a waxy crude isfirst charged to atmospheric fractionating tower 1 for the separation ofvolatae volatile A portion of a 350550F. fraction, taken off throughline 2, is bypassed through line 3 for use as a low pour cutter, as hasbeen described above. The residue leaving through line 4 is fed into avacuum tower 5, where an overhead waxy gas oil portion is separated. Theviscous pour residuum leaving through line 6 is converted into low pourfuel oil in accordance with the present invention.- It will beunderstood that the temperature employed in tower 5 will vary from onefeedstock to another, the controlling factor being the point where theresiduum goes from a predominatly waxy pour to a predominantly viscouspour.

FIG. 2 shows diagrammatically a process in which visbreaking is combinedwith the procedure shown in FIG. 1. The tower 1, line 2 and bypass line3 are the same as in FIG. 1 but the residue leaving the tower 1 throughline 14 is passed through a visbreaking furnace 15 where it is heated toincipient cracking. It is then discharged into an atmospheric flashtower 16, from which the partially cracked overhead product is returnedthrough line 17 to tower l for fractionation with the waxy crudefeedstock. The visbroken residuum leaves flash tower 16 through line 18and is fed into a vacuum tower 19, similar in operation to tower 5 ofFIG. 1, where an overhead waxy gas oil portion is separated Theresiduum, which for example may be the 850F.+ residuum of a Libyan waxycrude, leaves tower 19 through line 20 and now has a viscous pour. Ittherefore is converted into a fuel oil meeting the desiredspecifications by blending with the requisite quantity of the low pourcutter obtained from line 3.

In some instances, particularly in foreign countries it is often desiredto maximize middle distillate (furnace oil or diesel fuel) productionfrom a crude. Two procedures for accomplishing this objective are shownin FIGS. 3 and 4 of the drawings.

In the process shown diagrammatically in FIG. 3 the atmospheric reducedwaxy crude, such as a Libyan crude, is visbroken in a furnace 21 andcharged to atmospheric column 22 operating at atmospheric pressure,where gases, gasoline and a furnace oil or diesel fuel fraction areseparated. The stripped residue passes through line 23 to a vacuumdistillation column 24, the overhead fraction of which is passed throughline 25 to a thermal cracking furnace, 26. In this furnace it is heatedto a cracking temperature, after which it is recycled through line 27 toatmospheric after which it is recycled through line 27 to atmosphericcolumn 22 in admixture with further quantities of visbroken feed. Theresiduum from vacuum column 24, which now has a viscous pour, iswithdrawn through line 28 for blending with a low pour cutter such asa'fraction of the diesel or furnace oil boiling in the 350550F. range.

In a modification of this procedure the atmospheric reduced waxy crudeis not visbroken. The overhead from vacuum tower 24 would then be a waxygas oil which would be recycled to extinction through a visbreakerfurnace. To maximize middle distillates production, the residuum in line28, produced from the vacuum tower, would be a high IBP material 1,000F.IBP or greater), the quantity of which would be correspondingly reduced.By cutting a deep vacuum residuum in this manner the availablevisbreaker recycle would be increased, giving rise to greater productionof middle distillates from recycle thermal cracking heater 26.

In FIG. 4, a procedure somewhat similar to that of FIG. 3 is shown inwhich the thermal cracker on the recycle stream is replaced by acatalytic cracker. In this process the atmospheric reduced waxy crude isnot visbroken; it is introduced through feed line 31 into a vacuumdistilling column 32. A distillate from this column, having a 550650F.IBP, is withdrawn through line 33 and introduced into fluid catalyticcracking unit 34. In

I order to maximize middle distillate production, instead of gasoline,this cracker is operated at reduced severity. Thus, instead of obtainingabout 50 volume percent per pass of gas oil conversion to gasoline andlighter products, the per pass conversion is reduced to about 30 volumepercent or lower.

The "product's leaving catalytic cracker 34 through line 35 areseparated in the usual manner in atmospheric column 36, the bottomsbeing withdrawn through line 37 and recycled to extinction by admixturewith the catalytic cracker feed. The desired furnace oil or diesel fuelfraction is withdrawn through line 38 as a side stream from column 36.

The column 32 is operated at temperatures such that the residuum leavingthrough line 40 will have a viscous pour. Thus in the case of a reducedLibyan crude the residue in this line will have an IBP of at least 950F.

and preferably about 1,020F. The material in this line can therefore beconverted into a low pour fuel oil by blending with suitable quantitiesof low pour cutter, such as a suitable fraction obtained through line41.

Typical results obtainable by the processes of FIGS. 3 and 4 aredescribed in Examples 4 and 5, respectively.

The invention will be further described and illustrated by the followingspecific examples. It should be understood, however, that although theseexamples may describe some of the more specific features of ourinvention they are given primarily for purposes of illustration and theinvention in its broader aspects is not limited thereto.

Example 1 Low pour point cutter stocks suitable for use in practicingthe invention are obtainable from virgin and cracked light gas oils:

CUTTER NO. 1

This is a 350550F. fraction derived from an Amna virgin crude and hasthe following properties:

API Gravity 45.2 Viscosity, SUS at 100F. 32.1 Pour Point, F. 20 Sulfur,Wt. 0.091

CUTTER NO. 4

Thermal cracked 350-650F. gas oil:

APl Gravity 32.9 Viscosity, SUS at 100F. 333 Four Point, F. 31 20 5Sulfur, Wt. 0.25

CUTTER NO. 5

Thermal cracked 350-650F. gas oil:

AP! Gravity 32.4 Viscosity, SUS at 100F. 33.6 Pour Po m, F. -35

CUTTER NO. 6

This was a catalytically cracked 3505'50F. gas oil fraction. it has apour point of 85F.

CUTTER NO. 7

This was a catalytically cracked 350650F. gas oil fraction having a pourpoint of 10F.

The use of these cutters will be illustrated in subsequent examples. Itwill be understood, that, if desired,

they can be used in admixture with each other, or in admixture withother gas oils, to obtain cutter compositions having any desired pourpoint of 0F. or lower. Such mixtures are sometimes more compatible withcertain residua, and particularly with some visbroken residua, than aresingle gas oil fractions.

EXAMPLE 2 Typical fuel oils derived from Libyan crude are shown in thefollowing table.

TABLE 2 Blend Cutter Visc. Res Viscosity Pour SUS, Pour N0. IBP F. SUS,210 F. pt. (F.) No. Wt. percent 210 F. pt. F.)

850 508 100 4 20 Ill 75 850 508 100 4 51 950 2,250 140 4 20 192 9502.250 140 4 40 30 1020 11,000 160 4 20 447 50 1020 11,000 160 7 28 19730 1020 11,000 160 7 36 93 10 1020 11,000 160 6 30 146 35 CUTTER NO. 2The iiiiportance of converting the residua from waxy V V M" pour toviscous pour is evident from the above results. Thermal cracked 350650F.gas oil:

APl Gnavuty 35 5 EXAMPLE 3 ,121 02? 50 Visbreaking is a process in whicha petroleum feed- Sulfur, Wt. 0.35 Stock such as a topped crude 1sheated and thermally cracked slightly in a visbreaker furnace. It isdescribed, a for example, on page 154 of the September 1969 issue C T 3of Hydrocarbon Processing. We have found that vis- I i 55 breakingcracks or alters the wax in the vacuum resid- Thermal cracked 3SO-650F.gas om uum of a waxy crude and thus converts its pour charac- CP fi 00Fteristics from waxy to viscous. g Fuel oils obtained by cuttingvisbroken Libyan re- Sulfur. Wt. 0.36 sidua with low pour point cuttersare shown in Table 3.

TABLE 3 I Blend Cutter Visc. Resid. Viscosity Pour SUS, Pour No. lBP F.SUS, 21 R m No. Wt. percent 210 F. Pt. (F.)

EXAMPLE 4 Visbreaking With Recycle Thermal Cracking The process shown inFIG. 3 of the drawings was operated with a Libyan reduced waxy crudecharge using the following conditions:

" If the atmospheric reduced crude is not visbroken this yield ofresiduum increases to bout 42.5 column percent.

EXAMPLE Mild Catalytic Cracking at 920F. Reactor Temperature The processof FIG. 4 of the drawings was operated with the following material andresults;

Fresh Feed Recycle Recycle: Fresh Feed Volumn Ratio Per Pass F.F.Conversion Volume Percent (350F.)

Yields: Dry Gas Butanes Pentanes ll5l4 350F. Naphtha 350-650F. Gas OillO20F.+Residuum 6501020F. Gas Oil 650F.+Gas Oil Vol.

We claim:

1. A method of producing a low pour fuel from a waxy crude whichcomprises the steps of producing a viscous pour residuum from a waxycrude by subjecting a waxy pour atmospheric residuum obtained from thewaxy crude to visbreaking, separating the resulting product underatmospheric pressure into distillates and a residuum, subjecting theresiduum so obtained to a deep vacuum distillation to produce a viscouspour vacuum residuum having an initial boiling point of at least 1,020F.and mixing the viscous pour residuum so obtained with from about 15-45percent based on the weight of the mixture of a low pour cutter, havinga pour point not higher than OF., sufficient to produce a fuel oilhaving a pour point not higher than 50F. and

a viscosity within the range of about 50 to 240 SUS at 2. A methodaccording to claim 1 in which at least a portion of the distillate fromthe vacuum distillation is thermally cracked and the thermally crackedproduct so obtained is combined with the product of the visbreaking.

3. A method according to claim 1 in which the viscous pour residuum isproduced by vacuum distillation of a waxy crude feedstock at atemperature sufficiently high to produce a viscous pour residuum and thelow pour cutter is produced by cracking an overhead fraction from thesaid vacuum distillation.

4. The method according to claim 2 in which the cracking is fluidizedcatalytic cracking.

5. A method according to claim 1 in which the cutter is a 350550F. gasoil fraction.

2. A method according to claim 1 in which at least a portion of thedistillate from the vacuum distillation is thermally cracked and thethermally cracked product so obtained is combined with the product ofthe visbreaking.
 3. A method according to claim 1 in which the viscouspour residuum is produced by vacuum distillation of a waxy crudefeedstock at a temperature sufficiently high to produce a viscous pourresiduum and the low pour cutter is produced by cracking an overheadfraction from the said vacuum distillation.
 4. The method according toclaim 2 in which the cracking is fluidized catalytic cracking.
 5. Amethod according to claim 1 in which the cutter is a 350*-550*F. gas oilfraction.